VOA’s Mandarin Service correspondent was detained Monday evening by Chinese police as he was attempting to interview a retired Chinese professor who was taken away by authorities during a live television interview with VOA nearly two weeks ago.

Correspondent Yibing Feng was taken into custody in Jinan, Shandong province after talking to professor Sun Wenguang, 84, through a closed door of his apartment. Wenguang told Feng details of his detention and thanked VOA for allowing him to express his freedom of speech on the air.

Authorities in the apartment hallway attempted several times to disrupt the interview and ordered Feng and his Chinese assistant to leave the building. The two VOA staffers were then held by police at the building exit. They are still believed to be in police custody.

Sun Wenguang, who was detained earlier this month, was only recently allowed to return home under strict security, close friends told VOA on Monday. Chinese authorities have refused to comment on his detention.

The professor told the friends that after he was detained on August 1, he was moved to several locations including Yanzi Mountain Villa at Jinan Military Region, a military-linked hotel and reception center in Jinan, eastern China, his hometown. He was taken to four places, often staying for one or two days under a security watch, friends said.

Sun was taken away during a live telephone interview on the VOA Mandarin television show Issues & Opinions as he was criticizing China’s foreign aid and diplomatic strategy in Africa. During the interview, he told VOA that authorities were breaking into his house in an attempt to prevent him from speaking out against the government.

The professor returned home after more than 150 alumni of China's Shandong University - where he taught for decades - wrote an open letter to authorities, urging the school to ensure his personal safety and freedom.

Wang Shujun, a co-signer of the open letter, told VOA that he was shocked about the incident, which he thought was outrageous, uncivilized and unconstitutional. He noted that the local authorities in Jinan, the capital of Shandong province, severely hurt China's international image by treating the outspoken critic so rudely and recklessly.

"Even President Xi Jinping wouldn't be happy if he learned what happened to the professor," said Wang in a telephone interview with VOA Sunday.

Chinese authorities, including leaders of Shandong University, have kept silent about the incident involving professor Sun despite continuing inquiries from VOA and other international media.